Light responsive relay



P 1954 N. o. H. BERGLUND 2,689,889

LIGHT RESPONSIVE RELAY Filed March 20, 1952 I N VEN TOR //45 040/ ytz/vfz? 85%40/V0,

BY Qua.

ATTORNEY Patented Sept. 21 1954 LIGHT RESPONSIVE RELAY Nils Olof Helmer Bcrglund, Lidingo, Sweden, assignor to Svenska Aktiebolag'et Gasaccumulator, Lidingo, Sweden, a. corporation of Sweden Application March 20, 1952, Serial No. 277,660

Claims priority, application Sweden March 20, 1951 4 Claims. (01. zoo-81.02)

edges so as to allow them to bend in accordance with variations in the temperature. A contact device is adapted to be actuated in response to variations in the distance between the plates.

In order to eliminate the influence of fluctuations in ambient temperature the plates are disposed to bend in the same direction, whereby the distance between the plates remains constant as long as the dilference in temperature between them is constant.

The switch is preferably disposed between the plates and attached to one plate at its midpoint in such a manner that its operating knob may respond to pressure from the other plate. However, it may also be positioned on the outside of a plate, the actuating force being applied by means of a rod connected to the other plate.

An embodiment of the invention is described below with reference to the attached drawing, Fig. 1 of which shows the relay in elevation and Fig. 2 of which shows a top view of the relay.

In the drawing, reference numerals l and 2 designate a pair of parallel bimetal plates. The plates are supported at the corners on points 3 and are pressed against the points in any suitable way, for instance, as indicated in Fig. 1, by means of a clamp 4 provided with an adjustable screw pressing the plates I and 2 against the points 3. The points 3 and, in the illustrated embodiment, the clamps 4 are attached to distance pieces 9, whereby the spacing between the plates is maintained constant at the corners. In the interest of clarity only one of the clamps 4 has been illustrated.

The plates are arranged to bend in the same direction, for instance downwardly, upon a rise in temperature. As long as the plates have the same temperature the distance between their midpoints is therefore constant. If however one of the plates is more light-absorptive than the other and the plates are exposed to light, the more light-absorptive one of the plates will take on a somewhat higher temperature than the other plate. As a result, the distance between the midpoints of the plates changes and this change can be utilized for actuating a contact device.

In the embodiment shown, the plate I is more light-absorptive than the plate 2. It may for instance be a dull black and the plate 2 white or polished. When light is thrown on the plates, the plate I is therefore brought to a somewhat higher temperature than the plate 2 and is therefore bent more outward than the plate 2.

The contact device 5 which is to be actuated by the bimetal plates comprises a microswitch, which is of such a construction that the operating knob 6 thereof need only be displaced by a few tenths of a millimetre in order for the switch to operate. The operating force required is of the order of a few hundreds of grams. The operating knob 6 is actuated by a screw 1 passing through a bushing 8 at the midpoint of the plate I. The screw may be locked in any suitable way in its adjusted position. Adjustment should be made for the contact to be closed when the relay is in darkness or the illumination is below a predetermined value. Upon an increase in illumination the circuit is broken because the black plate I takes on a higher temperature and is therefore bent more outward, whereby the screw 1 is made to actuate the operating knob 6. If the illumination goes down below the predetermined value referred to, the plates resume their original shape and the contact is again closed.

In an arrangement of this kind it is of great importance that no erratic friction forces should be able to influence the movement of the plates, so that these are left to bend freely. This is because bending of a plate decreases the distance between the corners and the support therefore must be of such a construction as not to impede this movement of the plate. Also, the position of the supporting points at the plates must remain unchanged for varying degrees of bending. Only if this requirement is fulfilled will it be possible to achieve stable and dependable operation, so that actuation of the switch always takes place at a predetermined value of illumination. In the present case this was ensured through the supporting points 3 being attached to spacers 9 having a certain degree of freedom to move in a plane parallel to the plates.

It has been found suitable to attach the spacers 9 to leaf springs [0, which are supported by fixedly mounted supports ll. Each spring may be parallel with an edge of the plates. Owing to the springs In each one of the spacers is free to swing toward one of the adjacent spacers whereby the spacers are free to adapt themselves to the changes in distance between the corners of a plate that may occur in actual operation.

In the manufacturing process some differences may occur between the resiliency of individual plates, i.'e., between the extent to which they are bent in response to a predetermined temperature variation. In order to eliminate errors of this type, one or both plates may be associated with springs tending to increase or decrease the bending thereof in response to variations in ambient temperature. In the drawing a spring l2 of this kind is shown connected between the midpoint of one of the plates and the base I3.

The whole arrangement should preferably be encased in a transparent housing of glass, plastic material or the like.

What I claim is:

1. A light responsive relay, comprising, a pair of substantially parallel and rectangular bimetal plates having different light-absorbing characteristics, plate mounting members for supporting said plates at a plurality of points at the edges thereof, said mounting members being individually movable in a direction parallel to said plates, and a switch having two contact members, one contactmember being attached to the midpoint of one of said plates and the other contact mem-- ber being attached to the midpoint of the other of said plates, said switch being actuated through differential displacement of said plates.

2. A relay according to claim 1, in which said plate mounting members including points engaging said plates.

3. A relay according to claim 1, in which each one of said mounting members is supported by a leaf spring parallel with an edge of one of said plates thereby permitting movement of said one mounting member toward an adjacent mounting member.

4. A relay according to claim 1, comprising a spring attached to .one of said plates for changing the eifective resiliency thereof so as to provide substantially the same resiliency for both of said plates, whereby a predetermined temperature variation will cause substantially the same amount of bending of both plates.

References Cited in the file of this patent UNITED STATES PATENTS 

